I know this is a joke/meme, but I sincerely think of the Roman Empire a surprising amount of times. I find myself obsessing over how Roman citizens were living just as complex lives as we are today, or about Marcus Aurelius’ life and philosophy, or about how the Republic fell and became a totalitarian state.
… need you to elaborate on the concrete bit?
The Romans were really, really good at making concrete. Like most "ancient secrets", it's been overblown by sensationalist pop-historians, but they were still really good at it. IIRC they figured out that if you mix volcanic ash in with your concrete, it becomes stronger when exposed to water, not weaker.
edit: exposed, not exposed
Love it. Was learning about the ancient city of Ur. They had like indoor plumbing and stuff. Humans are incredible when external factors don't get in the way.